The field of the invention relates to the preparation of 1,2-benzisoxazole-3-acetic acid. Within that field, the present invention relates more particularly to a method for preparing 1,2-benzisoxazole-3-acetic acid comprising the step of reacting 4-hydroxy-coumarin with a hydroxyl-amine in the presence of a base.
Zonisamide is currently avaiable as an anti-epileptic agent which possesses anti-convulant and anti-neurotoxic effects. Zonisamide is also known as 1,2-benzisoxazole-3-methane sulfonamide or 3-(sulfamylmethyl)-1,2-benzisoxazole. It has the following chemical formula: 
The preparation of zonisamide is described in Japanese Pat. No. 53-77057 and Yakugaku Zasshi, 116(7), 533-47, 1996, both of which are incorporated herein by reference. These references teach a synthesis process of zonisamide that involves 4 or 5-steps, starting from 4-hydroxy-coumarin (4-HC). The synthesis of zonisamide occurs via the intermediates: namely, 1,2-benzisoxazole-3-acetic acid (BOA) and the sodium salt of benzisoxazole methane sulfonic acid (BOSxe2x80x94Na).
Many synthetic routes for preparing zonisamide have been described in the literature. One of the synthetic routes for preparing zonisamide is described in U.S. Pat. No. 4,172,896 and Japanese Pat. No. 53-77057 to Dainnipon. This particular synthetic route starts from 1,2-benzisoxazole-3-bromo-methane (zonisamide-bromide). The zonisamide-bromide is converted to 1,2-benzisoxazole-3-methane-sulfonic acid sodium salt (BOSxe2x80x94Na) in the reaction with sodium sulfite as is shown in the following scheme 1: 
Zonisamide-bromide is prepared according to the literature (Chem. Pharm. Bull., (Tokyo), 24, 632, 1976) by the bromination reaction of 1,2-benzizoxazole-3-acetic acid (BOA). BOA is prepared by Posner reaction (T. Posner, Chem. Ber., 42, 2523, 0913, T.Posner, and R.Hess, Chem. Ber., 46, 3816, 1913, M. Gianella, F. Gualtieri, C. Melchiorre and A. Orlandoni, Chem. Therap., 1972, 2, 127) and starts from 4-hydroxy-coumarin in the reaction with metallic sodium as shown in the following scheme 2: 
The Posner reaction for BOA preparation involves the use of metallic sodium. When metallic sodium is used in alcoholic solution, BOA is not the sole reaction product and the side-reaction product, O-hydroxy-acetophenone-oxime, is obtained in about 30%.
The high percentage of the side reaction products as well as the difficulty of using the aforementioned process on an industrial scale due to the use of metallic sodium render said process unfavorable, and thus the need for an improved process for preparing BOA and BOSxe2x80x94Na intermediates remains.
According to Dainnipon in the patent Japanese Pat. No. 53-77057, an alternative synthetic route for preparing zonisamide starts from 4-hydroxy-coumarin may occur via the same intermediates BOA and BOSxe2x80x94Na as shown in the following scheme 3: 
1,2-benzizoxazole-3-acetic acid (BOA), the product of the initial step after reacting 4-HC with NH20H (scheme 3), is converted to the intermediate BOSxe2x80x94Na in the sulfonation reaction with ClSO3H/dioxane in ethylene chloride at room temperature for about three hours followed by about 6 hours heating at about 50xc2x0 C. After the reaction is complete, water and NaOH are added and the product is isolated as sodium salt (BOSxe2x80x94Na) by evaporation of the aqueous layer. BOA and BOSxe2x80x94Na are the intermediates in the zonisamide preparation according to both synthetic schemes. All the cited references are incorporated by reference in their entireties herein.
An object of the present invention is to provide an improved process for preparing a salt of BOS (e.g., BOSxe2x80x94Na) with higher purity and lesser side-products.
Another object of the present invention is to provide an improved process for preparing a salt of BOS (e.g., BOSxe2x80x94Na) as an intermediate for the preparation of 1,2-benzisoxazole-3-methane sulfonamide (i.e., zonisamide).
Another object of the present invention is to provide an improved process for preparing a salt of BOS (e.g., BOSxe2x80x94Na) in which the sulfonation of BOA occurs in a solvent of methylene chloride (instead of ethylene chloride).
Another object of the present invention is to prepare 1,2-benzisoxazole-3-acetic acid (BOA) without the use of metallic sodium; and thus the process of this invention is substantially less hazardous.
Another object of the present invention is to prevent the formation of side-products, e.g., oximes; and thus, significantly increasing the yield of BOA, and substantially reducing the burden of removing the oxime side-product with ether, which by itself is hazardous.
Another yet object of the present invention is to prepare BOA or salts of BOS (e.g., BOSxe2x80x94Na); which are thereafter converted to 1,2-benzisoxazole-3-methane sulfonamide (i.e., zonisamide).
The present invention provides a process for preparing 1,2-benzisoxazole-3-acetic acid (BOA), comprising the step of reacting 4-hydroxy-coumarin (4-HC) with hydroxyl-amine in the presence of a base.
In a preferred embodiment, the base is selected from the group consisting of carbonate salts, aqueous ammonia, and organic bases. In another preferred embodiment, the carbonate salt is selected from the group of sodium carbonate (Na2CO3) and potassium carbonate (K2CO3). In another preferred embodiment, the organic base is an amine. More preferably, the amine is selected from the group consisting of triethyl-amine, tributyl-amine, and diethyl-amine.
In another preferred embodiment, the present invention provides a process for preparing 1,2-benzisoxazole-3-acetic acid (BOA), comprising the step of reacting 4-hydroxy-coumarin (4-HC) with hydroxyl-amine in the presence of a base, said process occurs in the presence of an alcoholic solvent.
Preferably, the alcoholic solvent is a lower alcohol. More preferably, the lower alcohol is selected from the group consisting of ethanol, methanol, n-butanol, iso-propyl-alcohol, iso-butanol, amyl-alcohol, and iso-amyl-alcohol.
In another preferred embodiment, the present invention provides a process for preparing 1,2-benzisoxazole-3-acetic acid (BOA), comprising the step of reacting 4-hydroxy-coumarin (4-HC) with hydroxyl-amine in the presence of a base and an alcoholic solution, wherein said process occurs at a temperature between room temperature and boiling point of the alcoholic solvent.
More preferably, the temperature of the reaction is between about 40xc2x0 C. and about 60xc2x0 C.
The present invention also provides an improved process of preparing a salt of benzisoxazole methane sulfonic acid, comprising the steps of: 1) sulfonating 1,2-benzisoxazole-3-acetic acid (BOA) using chlorosulfonic acid and dioxane in methylene chloride and sodium hydroxide solvents; and 2) isolating the salt of benzisoxazole methane sulfonic acid.
The present invention provides an improved process for preparing a salt of BOS (e.g., BOSxe2x80x94Na) in which the product is isolated by precipitatation from an aqueous solvent. Preferably, the precipitation is performed by salting-out with, e.g., sodium chloride. More preferably, the precipitation is performed by salting-out and and cooling.
In another preferred embodiment, the salt of BOS (e.g., BOSxe2x80x94Na) is isolated by evaporation.
Preferably, the salt of BOS may be isolated as BOS-Ba or BOSxe2x80x94Ca.
In another preferred embodiment, the preparation of the BOS-salt (e.g., BOSxe2x80x94Na) occurs at about 40xc2x0 C., preferably at about 55xc2x0 C. Preferably, the preparation of the BOS-salt is performed for a time duration of about 4 hours. More preferably, the preparation is performed for about 3, about 3.5 and about 5 hours.
According to the present invention, the reaction was improved as the reaction (for converting BOA to BOSxe2x80x94Na) is faster when methylene chloride is used. In other words, the reaction rate is faster when the solvent of the reaction is changed from ethylene chloride to methylene chloride.
As used herein, the following abbreviations are used: 1,2-benzisoxazole-3-acetic acid (BOA); benzisoxazole methane sulfonic acid (BOS); sodium salt of benzisoxazole methane sulfonic acid (BOSxe2x80x94Na); barium salt of benzisoxazole methane sulfonic acid (BOS-Ba); calcium salt of benzisoxazole methane sulfonic acid (BOSxe2x80x94Ca), chlorosulfonic acid (CISO3H); xe2x80x9corganic basexe2x80x9d refers to a base of carbon compounds; xe2x80x9croom temperatuerxe2x80x9d refers to ambient temperature of about 20xc2x0 C. to about 25xc2x0 C.
As disclosed in the present application, when methylene chloride was used to repeat the procedure as disclosed in Japanese Patent 53-77057, it was found that the reaction was substantially faster. The reaction was completed in about 12-17 hours of heating when ethylene chloride was used. In contrast, the reaction was completed in only about 3-5 hours at about 40xc2x0 C. when methylene chloride was used (See, the exp. #2337 and exp. #2356 in the Table 1).
According to the present invention, the process was further improved as it provides an alterative isolation procedure. It is known that the product (BOSxe2x80x94Na) can be isolated by evaporation of an aqueous phase. The present invention also provides two alternatives in which the product is precipitated from water which can be induced by the following ways; for example:
a) BOSxe2x80x94Na may be isolated from water by precipitation by salting-out; e.g., with sodium chloride (i.e., NaCI) and cooling; and
b) BOS-Ba or BOSxe2x80x94Ca may be isolated based on their low solubility, and can be quantitatively precipitated from water. Separation of BOS as the barium (Ba) or calcium (Ca) salt facilitates industrial scale preparation of this intermediate. Once the salt precipitates, it may be washed with water to reduce the inorganic salt content.
A product contaminated with inorganic salts is usually more hygroscopic than the pure compound; and, its use is problematic in the POC13 reaction.